2- Bromo-5-hydroxytryptophan

The stereochemistry of the modified tryptophan amino acids in the previously known konbamide and keramamide A sponge metabolites (/ ) has been determined to be l for both 2-bromo-5 -hydroxytryptophan and 6-chi oro-5 - hydro x v-/V-methyltryptophan, respectively (1066). However, based on synthetic studies, doubt has been raised as to the structure of konbamide (1067). A series of investigations of Okinawan Theonella sp. sponges has uncovered the new halo-genated keramamides, E (1031), H (1032) (1068), L (1033) (1069), M (1034), and N (1035) (1070). 

The Schollkopf intermediate was also used in the preparation of 2-bromo-5-hydroxytryptophan, using l-(f-butoxycarbonyl)-2-bromo-3-(bromomethyl)indole as the alkylating agent. <95TL9133>... 

With 1-hydroxytryptophan derivatives, similar substituent effects are observed (99H2815). In order to realize better yields of 5-substituted tryptophans, car-boxy and amino groups are transformed to ester and/or amide groups, choosing the 1-methoxy moiety as a leaving group. As a result, ( )-Ab-acetyl-5-chlorotryptophan methyl ester (219, 52%) is obtained together with 220 (7%) from ( )-218 by the reaction with aqueous HCl (Scheme 32). ( )-5-Bromo-Ab-methoxycarbonyltryptophan methylamide (222, 50%) becomes readily available... 

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